In an oil refinery, the removing of metals, such as mercury and iron, from crude oil has been practiced for many years. The crude may be contaminated with these metals from several sources, including, but not necessarily limited to:                Brine contamination in the crude oil as a result of the brine associated with the oil in the ground;        Minerals, clay, silt, and sand from the formation around the oil well bore;        Metals in the formation including, but not necessarily limited to, mercury, iron, calcium, zinc, silicon, nickel, sodium, potassium, etc.; and        Iron sulfides and iron oxides resulting from pipeline and vessel corrosion during production, transport, and storage.        
As noted, liquid hydrocarbon streams may be contaminated with mercury. Mercury imposes health and environmental hazards which must be dealt with in these contaminated streams. The mercury content also decreases the value of the hydrocarbon stream. Prior methods of removing mercury have utilized filtration and other means of mercury removal. However, usually the filtration process rate is hindered due to interference from water, solids and oil emulsions and/or interfaces which impede the process.
Further, much of the solids encountered during crude oil production consists of iron, most commonly as particulate iron such as iron oxide, iron (II) sulfide (FeS; ferrous sulfide), etc. As noted, other metals that are present and which may be desirably removed include, but are not necessarily limited to, mercury, copper, aluminum, calcium, zinc, silicon, nickel, sodium, potassium, and the like, and typically a number of these metals are present. Some of the metals may be present in a soluble form. The metals may be present in inorganic or organic forms. The presence of these metals can reduce the value of the crude and reduce the markets into which the hydrocarbon may be sold. Furthermore, the metals can introduce or affect a corrosion rate to other metals (such as aluminum) that is unacceptable. Finally, the disposal of mercury in oil production can become an environmental challenge, and create further restrictions on production rates.
In addition to complicating the crude oil management through the refining and more specifically the desalter operation, mercury, iron and other metals are of particular concern to further downstream processing. This includes the coking operation since iron and other metals remaining in the processed hydrocarbon yields a lower grade of coke. Removing the metals from the crude oil early in the hydrocarbon processing stages is desired to eventually yield high quality coke as well as to limit corrosion and fouling processing problems. Furthermore, some mercury contamination may be seen in other distillation fractions which can result in downstream corrosion and fouling issues in the downstream operations.
Several treatment approaches have been made to reduce total metal levels and these traditionally all center on the removal of metals at the desalter unit. Normally, the desalter only removes water soluble inorganic salts such as sodium or potassium chlorides. Some crude oils contain water insoluble metal organic acid salts such as calcium naphthenate and iron naphthenate, which are soluble or dispersed as fine particulate matter in the oil but not in water.
The metals present in crude oil are often in the form of metal salts and removing them is often performed in a desalter. Desalting involves the resolution of a natural emulsion of water that may accompany the crude oil by creating another emulsion in which about 2 to about 5 volume percent relative wash water is dispersed into the oil, typically using a mix valve. Alternatively, the crude oil may not comprise such a “natural emulsion”. The streams of desalted crude oil and effluent water are separately discharged from the desalter. The entire desalting process is a continuous flow procedure as opposed to a batch process. Normally, chemical additives, such as demulsifiers, are injected before the mix valve to help resolve the oil/water emulsion in addition to the use of electrostatic coalescence.
However, it would be desirable if metals such as mercury, among others, could be at least partially removed from liquid hydrocarbon streams using methods and equipment that are not desalters, but which could be used as an adjunct to a desalter. It would be further desirable to develop a composition and method employing it that would cause most or all of the mercury in crude oil to be removed from the crude oil prior to the desalter.